A description is presented of the clinical and pathologic features of the cardiotoxicity produced by doxorubicin and daunorubicin, two antineoplastic agents of the anthracycline family. The mechanisms by which these changes develop are reviewed, and new data concerning prevention of this cardiotoxicity are presented. These data show that the most effective means of blocking the cardiotoxicity is administration of ICRF-187 at the same time that anthracyclines are given.